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Sorkin, John

2026-Feb-28 05:08 UTC

[R] aggregate function does not work: arguments must have same length

PLEASE READ THIS ENTIRE MESSAGE. It explains my problem and contains a
reproducible example of the problem.

I am trying to run an aggregate function. The function produces the following
error message:
ERROR MESSAGE: 
Error in aggregate.data.frame(as.data.frame(x), ...) : 
  arguments must have same length

Everything beyond this line can be pasted into an R session and run:

####Start of code
#I am trying to write a code that will compute the number of hours for which we
have data for each day.
#Here are my data:

  inJan<-
    structure(list(NewTime = structure(c(1597363200, 1597366800, 
     1597370400, 1597374000, 1597377600, 1597381200, 1597384800, 1597388400, 
     1597392000, 1597395600, 1597399200, 1597402800, 1597406400, 1597410000, 
     1597413600, 1597417200, 1597420800, 1597424400, 1597428000, 1597431600, 
     1597435200, 1597438800, 1597442400, 1597446000, 1597449600, 1597453200, 
     1597456800, 1597460400, 1597464000, 1597467600, 1597471200, 1597474800, 
     1597478400, 1597482000, 1597485600, 1597489200, 1597492800, 1597496400, 
     1597500000, 1597503600, 1597507200, 1597510800, 1597514400, 1597518000, 
     1597521600, 1597525200, 1597528800, 1597532400, 1597536000, 1597539600
    ), class = c("POSIXct", "POSIXt"), tzone =
"UTC"), Days = structure(c(18488,
     18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 
     18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 
     18488, 18488, 18488, 18488, 18488, 18489, 18489, 18489, 18489, 
     18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 
     18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 
     18489, 18489, 18490, 18490), class = "Date")), class =
"data.frame", row.names = c(NA,-50L))
inJan
names(inJan)

#I have written a function which finds the number of hours between a last time
last(x) and a first time first(x).

# Number of follow-up hours in each day
timediff <- function(x) {
difftime(last(x),first(x),units="hours")
 }

#The function I wrote is used in an aggregate function which 
# finds the minimum and maximum time in each day, and then
# calls timediff to find the number of hours in each day.
zoop <-
aggregate(inJan[,"NewTime"],as.list(inJan[,"Days"]),timediff)

#When I run the aggregate function I receive and error:
#Error in aggregate.data.frame(as.data.frame(x), ...) : 
#arguments must have same length

#HOWEVER I believe inJan[,"NewTime"] and inJan[,"Days"] have
the same length

llength(inJan[,"NewTime"]) 
#[1] 50
length(inJan[,"Days"])  
#[1] 50

#Can someone tell my why the aggregate function thinks the arguments are a
different length?
#### End of code

Thank you,
John

John David Sorkin M.D., Ph.D.
Professor of Medicine, University of Maryland School of Medicine;
Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;?
Former PI Biostatistics and Informatics Core,?University of Maryland School of
Medicine Claude D. Pepper Older Americans Independence Center;
Senior Statistician University of Maryland Center for Vascular Research;

Division of Gerontology, Geriatrics and Palliative Medicine,
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
Cell phone 443-418-5382

Steve Martin

2026-Feb-28 05:53 UTC

head link

[R] aggregate function does not work: arguments must have same length

John,

The issue is the `as.list(inJan[,"Days"])` in the call to
`aggregate()`. This makes a list with 50 elements. Try
`list(inJan[,"Days"])` instead. Note that there is still an error, but
now coming from the `timediff()` function and unrelated to `aggregate()`.

Hope this helps.

Steve

On Saturday, February 28th, 2026 at 12:08 AM, Sorkin, John <jsorkin at
som.umaryland.edu> wrote:
> PLEASE READ THIS ENTIRE MESSAGE. It explains my problem and contains a
reproducible example of the problem.
> 
> I am trying to run an aggregate function. The function produces the
following error message:
> ERROR MESSAGE:
> Error in aggregate.data.frame(as.data.frame(x), ...) :
>   arguments must have same length
> 
> Everything beyond this line can be pasted into an R session and run:
> 
> ####Start of code
> #I am trying to write a code that will compute the number of hours for
which we have data for each day.
> #Here are my data:
> 
>   inJan<-
>     structure(list(NewTime = structure(c(1597363200, 1597366800,
>      1597370400, 1597374000, 1597377600, 1597381200, 1597384800,
1597388400,
>      1597392000, 1597395600, 1597399200, 1597402800, 1597406400,
1597410000,
>      1597413600, 1597417200, 1597420800, 1597424400, 1597428000,
1597431600,
>      1597435200, 1597438800, 1597442400, 1597446000, 1597449600,
1597453200,
>      1597456800, 1597460400, 1597464000, 1597467600, 1597471200,
1597474800,
>      1597478400, 1597482000, 1597485600, 1597489200, 1597492800,
1597496400,
>      1597500000, 1597503600, 1597507200, 1597510800, 1597514400,
1597518000,
>      1597521600, 1597525200, 1597528800, 1597532400, 1597536000, 1597539600
>     ), class = c("POSIXct", "POSIXt"), tzone =
"UTC"), Days = structure(c(18488,
>      18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488,
>      18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488,
>      18488, 18488, 18488, 18488, 18488, 18489, 18489, 18489, 18489,
>      18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489,
>      18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489,
>      18489, 18489, 18490, 18490), class = "Date")), class =
"data.frame", row.names = c(NA,-50L))
> inJan
> names(inJan)
> 
> #I have written a function which finds the number of hours between a last
time last(x) and a first time first(x).
> 
> # Number of follow-up hours in each day
> timediff <- function(x) {
> difftime(last(x),first(x),units="hours")
>  }
> 
> #The function I wrote is used in an aggregate function which
> # finds the minimum and maximum time in each day, and then
> # calls timediff to find the number of hours in each day.
> zoop <-
aggregate(inJan[,"NewTime"],as.list(inJan[,"Days"]),timediff)
> 
> #When I run the aggregate function I receive and error:
> #Error in aggregate.data.frame(as.data.frame(x), ...) :
> #arguments must have same length
> 
> #HOWEVER I believe inJan[,"NewTime"] and inJan[,"Days"]
have the same length
> 
> llength(inJan[,"NewTime"])
> #[1] 50
> length(inJan[,"Days"])
> #[1] 50
> 
> #Can someone tell my why the aggregate function thinks the arguments are a
different length?
> #### End of code
> 
> Thank you,
> John
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;
> Former PI Biostatistics and Informatics Core, University of Maryland School
of Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
> 
> Division of Gerontology, Geriatrics and Palliative Medicine,
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
> 
> 
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Peter Dalgaard

2026-Feb-28 07:27 UTC

head link

[R] aggregate function does not work: arguments must have same length

Untested, but maybe as.list() should be list()?

Sendt fra min iPhone
> Den 28. feb. 2026 kl. 06.08 skrev Sorkin, John <jsorkin at
som.umaryland.edu>:
> 
> ?PLEASE READ THIS ENTIRE MESSAGE. It explains my problem and contains a
reproducible example of the problem.
> 
> I am trying to run an aggregate function. The function produces the
following error message:
> ERROR MESSAGE: 
> Error in aggregate.data.frame(as.data.frame(x), ...) : 
>  arguments must have same length
> 
> Everything beyond this line can be pasted into an R session and run:
> 
> ####Start of code
> #I am trying to write a code that will compute the number of hours for
which we have data for each day.
> #Here are my data:
> 
>  inJan<-
>    structure(list(NewTime = structure(c(1597363200, 1597366800, 
>     1597370400, 1597374000, 1597377600, 1597381200, 1597384800, 1597388400,
>     1597392000, 1597395600, 1597399200, 1597402800, 1597406400, 1597410000,
>     1597413600, 1597417200, 1597420800, 1597424400, 1597428000, 1597431600,
>     1597435200, 1597438800, 1597442400, 1597446000, 1597449600, 1597453200,
>     1597456800, 1597460400, 1597464000, 1597467600, 1597471200, 1597474800,
>     1597478400, 1597482000, 1597485600, 1597489200, 1597492800, 1597496400,
>     1597500000, 1597503600, 1597507200, 1597510800, 1597514400, 1597518000,
>     1597521600, 1597525200, 1597528800, 1597532400, 1597536000, 1597539600
>    ), class = c("POSIXct", "POSIXt"), tzone =
"UTC"), Days = structure(c(18488,
>     18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 
>     18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 
>     18488, 18488, 18488, 18488, 18488, 18489, 18489, 18489, 18489, 
>     18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 
>     18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 
>     18489, 18489, 18490, 18490), class = "Date")), class =
"data.frame", row.names = c(NA,-50L))
> inJan
> names(inJan)
> 
> #I have written a function which finds the number of hours between a last
time last(x) and a first time first(x).
> 
> # Number of follow-up hours in each day
> timediff <- function(x) {
> difftime(last(x),first(x),units="hours")
> }
> 
> #The function I wrote is used in an aggregate function which 
> # finds the minimum and maximum time in each day, and then
> # calls timediff to find the number of hours in each day.
> zoop <-
aggregate(inJan[,"NewTime"],as.list(inJan[,"Days"]),timediff)
> 
> #When I run the aggregate function I receive and error:
> #Error in aggregate.data.frame(as.data.frame(x), ...) : 
> #arguments must have same length
> 
> #HOWEVER I believe inJan[,"NewTime"] and inJan[,"Days"]
have the same length
> 
> llength(inJan[,"NewTime"]) 
> #[1] 50
> length(inJan[,"Days"])  
> #[1] 50
> 
> #Can someone tell my why the aggregate function thinks the arguments are a
different length?
> #### End of code
> 
> Thank you,
> John
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;
> Former PI Biostatistics and Informatics Core, University of Maryland School
of Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
> 
> Division of Gerontology, Geriatrics and Palliative Medicine,
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
> 
> 
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Rui Barradas

2026-Feb-28 08:40 UTC

head link

[R] aggregate function does not work: arguments must have same length

?s 05:08 de 28/02/2026, Sorkin, John escreveu:> PLEASE READ THIS ENTIRE MESSAGE. It explains my problem and contains a
reproducible example of the problem.
> 
> I am trying to run an aggregate function. The function produces the
following error message:
> ERROR MESSAGE:
> Error in aggregate.data.frame(as.data.frame(x), ...) :
>    arguments must have same length
> 
> Everything beyond this line can be pasted into an R session and run:
> 
> ####Start of code
> #I am trying to write a code that will compute the number of hours for
which we have data for each day.
> #Here are my data:
> 
>    inJan<-
>      structure(list(NewTime = structure(c(1597363200, 1597366800,
>       1597370400, 1597374000, 1597377600, 1597381200, 1597384800,
1597388400,
>       1597392000, 1597395600, 1597399200, 1597402800, 1597406400,
1597410000,
>       1597413600, 1597417200, 1597420800, 1597424400, 1597428000,
1597431600,
>       1597435200, 1597438800, 1597442400, 1597446000, 1597449600,
1597453200,
>       1597456800, 1597460400, 1597464000, 1597467600, 1597471200,
1597474800,
>       1597478400, 1597482000, 1597485600, 1597489200, 1597492800,
1597496400,
>       1597500000, 1597503600, 1597507200, 1597510800, 1597514400,
1597518000,
>       1597521600, 1597525200, 1597528800, 1597532400, 1597536000,
1597539600
>      ), class = c("POSIXct", "POSIXt"), tzone =
"UTC"), Days = structure(c(18488,
>       18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488,
>       18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488,
>       18488, 18488, 18488, 18488, 18488, 18489, 18489, 18489, 18489,
>       18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489,
>       18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489,
>       18489, 18489, 18490, 18490), class = "Date")), class =
"data.frame", row.names = c(NA,-50L))
> inJan
> names(inJan)
> 
> #I have written a function which finds the number of hours between a last
time last(x) and a first time first(x).
> 
> # Number of follow-up hours in each day
> timediff <- function(x) {
> difftime(last(x),first(x),units="hours")
>   }
> 
> #The function I wrote is used in an aggregate function which
> # finds the minimum and maximum time in each day, and then
> # calls timediff to find the number of hours in each day.
> zoop <-
aggregate(inJan[,"NewTime"],as.list(inJan[,"Days"]),timediff)
> 
> #When I run the aggregate function I receive and error:
> #Error in aggregate.data.frame(as.data.frame(x), ...) :
> #arguments must have same length
> 
> #HOWEVER I believe inJan[,"NewTime"] and inJan[,"Days"]
have the same length
> 
> llength(inJan[,"NewTime"])
> #[1] 50
> length(inJan[,"Days"])
> #[1] 50
> 
> #Can someone tell my why the aggregate function thinks the arguments are a
different length?
> #### End of code
> 
> Thank you,
> John
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;
> Former PI Biostatistics and Informatics Core,?University of Maryland School
of Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
> 
> Division of Gerontology, Geriatrics and Palliative Medicine,
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
> 
> 
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.Hello,

The problem is not in the input vectors' lengths, it's the output
length.

When aggregating, I find it better to use the formula interface.
It avoids the list() call and eventual errors due to as.list() being 
mistaken for it.

Also, when using non base packages, please include a call to library() 
or similar. I had to revise the function for it to work.


# Number of follow-up hours in each day
timediff <- function(x) {
   difftime(dplyr::last(x), dplyr::first(x), units = "hours")
}

aggregate(NewTime ~ Days, inJan, timediff)
#>         Days  NewTime
#> 1 2020-08-14 23 hours
#> 2 2020-08-15 23 hours
#> 3 2020-08-16  1 hours


Alternative versions:

# This is what Peter Daalgard proposed (list, not as.list)
aggregate(inJan[,"NewTime"], list(inJan[,"Days"]), timediff)

# another one
aggregate(inJan[["NewTime"]], list(inJan[["Days"]]),
timediff)


# not relevant, but if you ever want just a vector, here it is.
tapply(inJan[,"NewTime"], inJan[,"Days"], timediff)
#> 2020-08-14 2020-08-15 2020-08-16
#>         23         23          1


Hope this helps,

Rui Barradas

R help - Feb 2026 - aggregate function does not work: arguments must have same length

[R] aggregate function does not work: arguments must have same length

[R] aggregate function does not work: arguments must have same length

[R] aggregate function does not work: arguments must have same length

[R] aggregate function does not work: arguments must have same length